Abstract

The present experimental study aims to investigate condensation heat transfer characteristics of R600a/oil/multi-walled carbon nanotube (MWCNT) nano-refrigerant flow inside a horizontal micro-fin tube. The test condenser is a horizontal double-pipe heat exchanger consists of a copper micro-fin tube with 14.18 mm inner diameter which is installed in a polyethylene shell with a diameter of 6 cm. The experiments cover a wide range of parameters, including mass velocity of 54 to 90 kg/m² s, vapor quality of 0.03 to 0.76, and condensation pressure of 550 to 700 kPa. The investigations are conducted in three parts, including the characteristics of pure R600a condensing flow inside micro-fin tubes, the effect of adding lubricating oil with concentration of 1%, and the impact of adding nano-oil with nanoparticles compactness of 0.1, 0.2, and 0.3%. Comparison of the experimental data for the pure refrigerant flow with three well-known correlations shows the maximum deviation of ±20% which validates the test procedure. Based on the results, R600a/oil heat transfer coefficient is higher than pure R600a in low and medium vapor qualities, while at high qualities the pure R600a shows higher coefficient due to the impact of lubricating oil on the condensate liquid film thermal resistance. In addition, adding nanoparticles is more effective at low and medium vapor qualities and high mass velocity. The results showed that using MWCNT nanoparticles with the compactness of 0.3% increases the heat transfer coefficient up to 74.8% in comparison to the pure refrigerant.

中文翻译：

---

R600a /油/ MWCNT纳米制冷剂在微翅片管内冷凝流动的实验研究

摘要

本实验研究旨在研究水平微翅片管内R600a /油/多壁碳纳米管（MWCNT）纳米制冷剂的冷凝传热特性。测试冷凝器是卧式双管热交换器，由内径为14.18 mm的铜微翅片管组成，该管安装在直径为6 cm的聚乙烯外壳中。实验涵盖了广泛的参数，包括54到90 kg / m ^2的质量速度 s，蒸汽质量为0.03至0.76，冷凝压力为550至700 kPa。研究分三个部分进行，包括纯R600a在微翅片管内的冷凝流动特性，添加浓度为1％的润滑油的效果以及添加纳米级致密性为0.1、0.2的纳米油的影响，和0.3％。将纯制冷剂流量的实验数据与三个众所周知的相关性进行比较，得出最大偏差为±20％，这验证了测试程序。根据结果​​，在中低蒸汽质量下，R600a /油的传热系数高于纯R600a，而在高质量下，由于润滑油对冷凝液膜热阻的影响，纯R600a表现出较高的系数。此外，在中低蒸汽质量和高质量速度下，添加纳米颗粒更有效。结果表明，与纯制冷剂相比，使用密度为0.3％的MWCNT纳米颗粒可使传热系数高达74.8％。